1. Field of the Invention
The present invention relates to a method for determining the compensation value of the width of a wire to be formed on a printed circuit board, and more particularly, to a method for determining the compensation value of the width of a wire by measuring the resistance of the wire.
2. Description of Related Art
Because of advanced electronic technology, the operational speed of electronic element such as integrated circuit chips has increased rapidly. Therefore, the electrical performance of the PCB (printed circuit board) with integrated circuit chips has to be improved to meet the requirements of the high-speed electronic elements. Particularly, the width of the wire that is formed on the PCB board has to be precisely controlled during the process of manufacturing a PCB board. The actual width of the wire formed on a PCB board is usually different from the one the film provided for producing the PCB board. That is, the wire formed on a PCB board may be over-etched or under-etched. The difference in width between the wire on the film and the wire actually formed on the PCB board is known as side-etching distance .sigma.. Side-etching distance .sigma. may influence the electrical performance of a PCB board. Therefore, compensation for side-etching distance .sigma. has to be provided in advance so that the desired wire width can be obtained when the wires are actually formed on the PCB board.
To make a proper compensation, the side-etching distance .sigma. has to be found by the following expression: .sigma.=W (width of the wire patterned on the film) .+-.W (width of the wire formed on the PCB board). A conventional method to obtain the side-etching .sigma. is to take a cross-section step to locally cut off the wire formed on the PCB board and use a microscope to measure the width of the wire so that the side-etching distance .sigma. can be found by using the above expression. However, the method suffers the following disadvantages:
1. High Error Possibility: The measurement of width is only made to a small portion of the wire. The measured value does not represent the average width of the entire wire. PA1 2. Time Consuming: The cross-section step requires lots of time to complete. Normally, it takes 15 minutes for a cutting operation, and the cut PCB board sample has to be cured, which takes another 25 minutes. PA1 3. Waste of Material: The cut PCB board sample is useless after measurement and has to be thrown away. PA1 4. Pollution: When the cut PCB board is cured, a chemical agent is required, which may cause pollution to the environment.
Accordingly, there is a need for the above method to be improved.